In the paper, a general category based approach to invertible Darboux transformations is sug gested. For operators of arbitrary dimension and arbitrary order, it is suggested to consider Darboux transfor mations of certain type, namely, of type I. Explicit compact formulas are obtained. In particular, any invert ible Darboux transformations of first order and, for example, Laplace transformations are type I transforma tions. For operators of third order in the plane, analogues of the Darboux transformation chains are obtained.